A petrochemical approach to discrimination between ortho- and para-metamorphites

Abstract

There are a variety of approaches to the restoration of the primary rocks, but various discrimination diagrams or functional formulae have a limit on their application and discrimination accuracy. On the basis of statistical analyses in conjunction with the advantages of various discrimination diagrams, this paper presents a new functional discriminant:

$$Dy = - 2 lg A + lg E - 0.5 lg F - 2 lg M + 3 lg C + 5.5 lg N + 1.5$$

The above discriminant can be rewritten as:

$$Dy = lg\frac{{EC^3 N^{5.5} K^{1.5} }}{{A^2 F^{0.5} M^2 }} - Z$$

This discriminant is not applicable to sedimentary rocks, particularly those enriched in Ca, and Mg rich ultrabasic rocks.

In this study 1640 typical rock samples and 126 sedimentary (metasedimentary) rock samples and 126 volcanogenic iron ore samples were tested with the above described discriminant. The results obtained are satisfactory with the exception of feldspar sandstone. The discrimination rates for various types of rocks are in the range of 85–95% or more with a total discrimination rate of 91.7%.

This paper analyzes the factors leading to wrong discrimination and also points out that coarse detrital rocks, weathered volcanic rocks, volcanic fine detrital rocks of two different material sources and Ca-rich sedimentary rocks are easy to suffer wrong discrimination.